Use of liquid smoke solutions as a replacement for smoking food by direct contact with wood smoke has become a standard industry practice. When applied to the surface of meats and other proteinaceous foodstuffs, liquid smoke will give an item a characteristic smoke flavor and produce a dark smoked color. The achievement of a smokehouse like product by application of an aqueous smoke solution to food requires the control and balancing of many related variables such as the food composition, temperature, humidity, processing and contact time, amount and concentration of smoke applied.
For example, when applying current aqueous smoke to meats the processor must compromise the smoke color of the product to keep the flavor at a desired level because the flavor imparting ability of known compositions is too intense at a given color. There is a need in the industry for an aqueous smoke solution with good coloring properties but with less intense flavoring ability.
Wood smoke is a complex and variable mixture of chemicals produced during pyrolysis and includes vaporous compounds which are normally liquid at room temperature. Pyrolysis is a general term for the thermal decomposition of any organic material such as wood, plants, and fossil fuels, which occurs either during combustion or in the absence of combustion. Combustion uses the oxidation or burning of a portion of the organic matter to provide the thermal energy required to vaporize and decompose the remainder. For pyrolysis without combustion, thermal energy must be supplied indirectly from some other source, such as radiation, solid or gaseous heat carriers, or thermal conduction through reactor walls. The energy vaporizes and decomposes the organic matter without burning the organic matter directly.
Either method of pyrolysis produces condensable liquids, non-condensable gases and solids in varying proportions depending upon reaction conditions. The condensable liquids can be further subdivided into water soluble organics and water insoluble tars. It is known that the desirable active ingredients for flavoring foodstuffs are among the water soluble condensable liquids.
While there are hundreds of different chemical species present in liquid smoke, liquid smoke components are generally divided into classes based on chemicals with distinct functional groups. These classes are acids, carbonyls, phenols, and basic and neutral constituents. In general, phenols are the primary flavoring compounds, carbonyls are mainly responsible for coloration and acids are principally preservatives and pH controlling agents. Acids and carbonyls also make a secondary contribution to flavor and enhance the surface characteristics of smoked meat products.
Both the color and flavor chemistry of liquid smoke compositions is highly complex as evidenced by the over four hundred compounds identified as constituents of these compositions. A summary of the many constituents found in liquid smoke is listed by Maga in "Smoke in Food Processing" CRC Press, pp. 61-68 (1968). A majority of researchers skilled in the art of smoke solutions have concluded that phenols are the important contributors to smoke aroma and flavor, however, minor amounts of certain types of compounds may significantly impact both the color and flavor chemistries of a particular composition.
For example, a representative commercially available smoke flavoring with a titratable acidity level of about 11% contains about 13% carbonyls, 1.5% phenols and at least 70% water. The remaining constituents, about 4.5% of the total mass balance of the smoke, include basic and neutral organic compounds. Reductions of both phenols and basic constituents by the process of this invention gives improved aqueous smoke solutions.
A reduction of the total phenolic component of an aqueous smoke mixture may produce a less flavorful smoke solution but still retain desirable coloring properties. Phenolic reduction gives a less flavorful smoke solution, however, even a solution with a significant weight reduction of phenols still retains substantial flavoring components. In addition, a reduction in selective basic constituents also gives an improved, less intensely flavored solution.
Where surface coloring is important, a measure of active carbonyls in a solution may determine the quantity of liquid smoke required. The active carbonyls initially react with the available amino groups on surface proteins of foodstuff. Subsequent reactions occurring under drying and heating conditions lead to formation of the characteristic brown smoked color The concentration of a specific carbonyl, hydroxyacetaldehyde, is also a good indicator of the color forming potential of liquid smoke.
A further measurement that is used to characterize liquid smoke is the browning index defined according to procedures described below. The browning index is used in the smoke flavoring industry to measure the browning performance of a liquid.
In commercially produced aqueous smoke solutions, production begins with smoke made by pyrolysis and limited combustion of wood which is subsequently collected in recirculating water columns. A typical commercial liquid smoke preparation for surface applications is the aqueous smoke flavoring described in U.S. Pat. No. 3,106,473 to Hollenbeck. The dilution of the condensable smoke components in water results in the removal of undesired tars and water insoluble components, however, further refinement of the solution is needed for the flavoring and coloring applications described above.
A number of methods to reduce the concentration of flavor producing phenols are disclosed in the art. One method uses liquid-liquid extraction with vegetable oils as described in U.S. Pat. No. 3,480,446 to Hollenbeck. With this method total phenolics can be reduced by about 55% using repeated extraction. The '446 patent, however, does not teach browning foodstuffs with the disclosed smoke flavored oils and the oil extraction process is not selective, desired as well as undesired components are removed by the process.
U.S. Pat. No. 4,431,033 to Nicholson teaches liquid-liquid extraction of aqueous smoke solutions with solvents which are immiscible in the aqueous solution. The .033 patent specifies that the solvent hydrogen bonding solubility parameter must be at least 2.7. The resulting extracted solution is described as tar depleted. While tar reduction is the object of the .033 patent, the total phenolics concentration is also reduced. The major shortcomings of the process include a high level of solvent retention and the extraction of desired as well as undesired components from the smoke solution.